The Nether Lands is the land just outside of Equestria, and where the Midnight Palace is located. The ponies had to travel through the Nether Lands during the Everstorm that occurred in My Little Universe: Supernova, and it's where Celestia was killed in.
Layout[]
While not too detailed in description, the Nether Lands are described as being more like Earth than Equestria, as pony magic isn't prominent here, and as such it wasn't as well-kept and maintained. Most of the Nether Lands is dry and barren with open fields. Equestria and the Nether Lands are split by a deep canyon.
History[]
Season 1[]
It's briefly seen in S01Ep11: Logical Care, when Cadance and Twilight Sparkle had to find a "cure" for Discord, and to face a Tatzlwurm just along the borders.
My Little Universe: Supernova[]
After Equestria became decimated by Parasprites, many ponies, including the princesses of Equestria, had to travel through the Nether Lands to reach the Midnight Palace. As they traveled through, they were constantly stalked and assaulted by the Sigbin, who kills one of the ponies and ultimately killed Celestia.